NSW HSC Biology

Reproduction is how a species continues once its individuals die. Organisms do it in two ways that differ in what they do to genetic variation, and most of the differences between groups come down to how that variation is traded against speed and energy cost. ## Asexual and sexual reproduction In **asexual reproduction** one parent produces offspring without gametes and without fertilisation. The offspring are produced by mitosis, so they are genetically identical to the parent and to each other (clones), apart from any new mutations. Because no mate has to be found and no gametes have to meet, populations can grow very quickly when conditions suit the parent. The disadvantage is that a population of clones has almost no variation, so a change such as a new disease or a shift in climate can affect every individual in the same way. In **sexual reproduction** two gametes, usually from two parents, fuse in **fertilisation** to form a zygote. Gametes are made by meiosis, which shuffles alleles, and fertilisation combines alleles from two parents, so the offspring differ from each other and from both parents. That variation is what natural selection acts on, and it is why sexually reproducing species are better placed to survive when the environment changes. The cost is that it is slower and uses more energy, because gametes must be made, a mate found and the gametes brought together. | Feature | Asexual | Sexual | |---|---|---| | Parents | one | usually two | | Gametes and…